In order to function well in the language being learned, it is important to understand the meanings and functions of adequate numbers of words and be able to use them appropriately. However, most of the students of XI Teknik Gambar Bangunan A (TGBA) class in SMKN 2 Depok found it difficult to deal with English because of their limited vocabulary. The observation results showed that they did not perform well in their test because they did not know the meanings of some words. They also did not know that similar words could carry different meanings or could be categorized into different parts of speech.

The research aimed to overcome the problem related to the limited vocabulary of XI TGBA students. Word games were chosen as the solution to the problem since they suited the learners’ characteristics. Word games were intended to help the students to acquire and recognize English words and their meanings as well as to categorize the words into the correct parts of speech. The problem that the researcher tried to answer was how word games helped XI TGBA students of SMKN 2 Depok improve their vocabulary mastery.

This research used Class Action Research (CAR) method. The research participants were 31 students of XI TGBA class in SMKN 2 Depok, Sleman, Yogyakarta in the 2011/2012 academic year.There were three cycles in this research; each cycle was completed in one meeting. The instruments used to gather data were students' personal pre-implementation and post-implementation vocabulary list, observation checklist, field notes, questionnaire and interview.

From the data analysis, it was found that word games motivated the students to participate actively in the learning process and to grow interest in learning English. The number of students writing correct words, meanings, and parts of speech after the implementation of the games increased. The percentage of correct number of words, meanings, and parts of speech written in their vocabulary list also increased. Teachers are encouraged to use word games to add variety to the lesson and adapt the most suitable procedures to be implemented in their classroom.